Our long-term goal is to extend the preservation time of kidneys utilizing recently developed techniques of hypothermic perfusion and cryopreservation. The objective of the proposed research would consequently be: 1) to obtain uniform cooling throughout a kidney by using a new perfusion system involving intravascular gas perfusion in combinations with liquid reperfusion, 2) to examine the cryopreservation of canine kidneys by avoiding crystal formation and maintaining the organs at a supercooled state, and 3) to examine factors influencing the rate and uniformity of rewarming the kidney in an effort to recover viable organs from the supercooled state. Following an initial perfusion of 500 ml of cryoprecipitated plasma with 12.5% DMSO, a cold intraarterial gas will be circulated throughout the kidney under controlled pressure to further reduce the core temperature. The kidney will thus be supercooled to a maximum of minus 40 degrees C. (The cooling limits of the new perfusion system) at rates of 0.5 degrees C to 4 degrees C/minute. Various gaseous cooling agents including helium (anoxic model) and oxygen will be evaluated to determine effects on tissue ATP stability. The kidney will be stored within the preservation unit at various temperatures ranging from minus 0.5 degrees to 4 degrees C/minute using either 1) circulation of warm gas, or 2) microwave heating, followed by liquid perfusion. This liquid perfusate consisting of 500 cc cryoprecipitated plasma with 2.5% DMSO, reduces the tissue concentration of DMSO to non-toxic levels, when the kidney core temperature is above 0 degree C. All kidneys are reimplanted into a subcutaneous pocket in the animals' groin after appropriate needle biopsies for electron microscopy and ATP assays are obtained. Serum levels of blood urea nitrogen and creatinine are determined daily after contralateral nephrectomy in the dogs. Different extents of supercooling ranging from minus 0.5 degrees to minus 4 degrees C will be considered.